Railway signaling system



4 Sheets-Sheet 1 H15 AI TORNEY H. A. THOMPSON RAILWAY SIGNALING SYSTEM Flled Feb 17 1940 May 19, 1942.

ay 19, 1942- H. A. THOMPSON RAILWAY SIGNALING SYSTEM Filed Feb. 17, 1940 4 Sheets-Sheet 2 R Y m, w m m V7 .T m d Mr s p 1 wm H 1 m y ,1 H. A; THOMPSON 2,283,297

RAILWAY SIGNALING SYSTEM 4 Sheets-Sheet 5 INVENTOR Filed Feb. 17, 1940 lgo il/ar .Thompmn.

HIS Ai'TORNEY May 19, 1942. H. A. THOMPSON RAILWAY SIGNALING SYSTEM 4 Sheets-Sheet 4 Filed Feb. 17, 1940 Patented May 19, 1942 RAILWAY SIGNALING SYSTEM Howard A. Thompson, Edgewood, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application February 17, 1940, Serial No. 319,510

7 Claims.

My invention relates to railway signaling systems for use on stretches of two direction running track and it has special reference to systems of this class wherein signals positioned along the wayside are controlled over line wires that extend between signal locations.

Generally stated, the object of my invention is to reduce the number of control conductors which line wire systems of railway signaling require.

A more specific object is to utilize a single pair of line wires to control signals that govern traffic in either direction.

Another object is to provide new and improved facilities for overlapping the track circuit control limits of the system signals and for approach controlling the energization of those signals.

An additional object is to protect against unsafe signal response upon an accidental crossing or breaking of the system line wires.

A further object is to make a new and novel application of the coded feed back" principle of Frank H..Nicholson Patent No. 2,021,944. 7 V

A still further object is to provide improved apparatus for use in line and other circuits of the coded feed back type.

In practicing my invention I attain the above and other objects and advantages by arranging the line circuits of the signaling system to operate on the coded feed back principle of the spcnsive to track relays which indicate the conditions of traffic in preselected sections of the signaled stretch; and governing the system signals by the coded energy which the thus controlled line circuits transmit.

I shall describe one form of railway signaling system which embodies the improvements of my invention and shall then point out the novel features thereof in claims. This illustrative embodiment is disclosed in the accompanying drawings in which:

Figs. 1a to 1c are diagrammatic views which, when placed end to end in the order named, show a stretch of two direction running track that is equipped with an overlap signaling system controlled in accordance with the teachings of my invention;

Fig. 2 is a single line diagram showing the limits of track circuit control for each of the several wayside signals in the system of Fig. 1;

Fig. 3 is a representation of one of the coded feed back line circuits by which the signals of Fig. 1 are controlled; and V Fig. 4 is a representation of Master and Feed back codes which are suitable for operating the line control circuits of Figs, 1 and 3. I In the several views of the drawings like reference characters designate corresponding parts. To facilitate the. description of the various circuit diagrams of these views, it will be assumed that the left end thereof is west and the right end east. Hence, train movements in the direction of from left to right will be spoken of as eastbound{ and movements in the direction of from right to left will be spoken of as westboundT.

Referring first to the composite diagram of Figs. la-c, the improvements of my invention are there disclosed as being incorporated in an opposing overlap system ofwayside signaling for a stretch of single track l2 over which traflic may move in either direction. At suitable intervals along this stretch the usual passing sidings PS (only one is shown in Fig. 1) are'provided. These sidings permit traffic to be diverted from the main track (under the customary control of end switches W) at proper times.

The rails of this two direction running stretch of single track l'2 are divided by the usual insulated joints 3 into the customary plurality of successive track sections I-II, II-III, IIIIlIa, IIIa/IV, etc. and the rails of each of these sections form a part of a steady energy track circuit which includes a track battery TB at one end of the section and a track relay TR at the opposite end. Each of these track relays responds to'the traffic conditions of the associated section in the customary manner; that is, the relay stays picked up as long as the section remains vacant and releases when the section becomes occupied.

Positioned at the locations I, II, III, IV, VI and VIII are wayside signals SE which are arranged to govern eastbound traffic through the track stretch. Similarly installed at the locations VII,-

home devices which display one or another of the indications of clear and stop while the remaining are distant devices which display one or another of the indications of clear and approach.

Included in the former or home signal class are the square ended semaphores SE-I-III- IV-VI and SWVIIIIVIIIII of Fig. 2 and the corresponding G--R (green-red) color light signals of Fig, 1; included in the latter or distant signal class are the notch ended semaphores SEIIIII-VIII and SW-V-IV-I of Fig. 2 and the corresponding G--Y (greenyellow) color light signals of Fig. 1.

In the composite diagram of Fig. 1 certain non-signal locations of track section division have also been shown. These are designated as IIIa, Va and WM and each marks a cut in the main signal block in which it is included. Such cuts may, of course, be occasioned byexcessive block lengths, by highway intersections (not shown) or for any other reason; due to their special character they have no wayside signals associated therewith.

As herein represented, the just named cut cations are utilized by the opposing overlap scheme of signal control in connection with which the improvements of my invention are disclosed. For an understanding of the basic features of this scheme reference to the control limit diagram of Fig. 2 may be made.

In that diagram the thin arrow lines emanating from the large dots at the signal locations indicate the limits of track circuit control for the wayside signals with which these lines are identified. For example, eastbound home signal SEIII which guards block III-IV is controlled as far to the east as location V and westbound home signal SWIV which guards the same block is controlled as far to the west as location II; eastbound signal SEIV at the west endof track length IVVII is controlled as far to the east as cut location VIIa. and westbound signal SWVII at the east end of the same track length is controlled as far to the west as location IV; etc.

It will be seen, therefore, that in its broader aspects this overlap arrangement of Fig. 2 is conventional in that: (1) the control of each home signal is extended beyond the next signal in advance (which governs in the same direction) for at least braking distance; and (2) the function of this overlapped control is to prevent opposing trains from entering the same block at the same time and colliding head on. Inasmuch as the broad principles of overlap control are well known in the art, no further description of them will here be attempted.-

The improvements of my invention are directed to the facilities by which the overlap control of Fig. 2 and other equivalent forms of signal governing may be effected. As shown in Fig. 1, these facilities include line circuits which extend between signal locations in conventional manner and which transmit energy for controlling the system signals.

Coded Zine circuits circuit including line wires 9 and I0 transmits the energy by which signal SEII is controlled; a fourth circuit including line wires l2 and I3 transmits the energy by which the home units G-R of signals SEIII and SWIV are controlled; a fifth circuit including line wires l4 and I5 transmits the energy by which the distant units G-Y of signals SEIII and SWIV are controlled; a sixth circuit including line wires l6 and I1 transmits the energy by which the signals SEIV and SWVII are controlled; a seventh circuit including line wires l8 and 19 transmits the energy by which signal SWV is controlled; an eighth circuit including line wires 20 and 2| transmits the energy by which signal SEVI is controlled; and a ninth circuit including line wires 22 and 23 transmits the energy by which signal SEVIII is controlled.

The signal control energy which each of the nine line circuits of Fig. l transmits is periodically interrupted or coded and it thus takes the form of recurring on period pulses that are separated by off period intervals. While these pulses may recur at any suitable rate, code speeds of 75 and pulses per minute are preferred.

One obvious advantage of selecting such standard rates is that the coding of the line circuit energy then may be effected by code transmitters of the conventional type represented at CT15 and CTIBU in Fig. 1. When such transmitters are used codes of the characters shown in Fig. 4 are produced.

In regard to the number of different forms of coded energy which the circuit conductors transmit, various of the line circuits of Fig. 1 differ from the remaining. In the case of each of the line circuits 56, 9-H], I8I9 and 2223, this transmitted energy is of the Master 75 code of Fig. 4 only; in the case of each of the line circuits '!8, Iii-l1 and 202l, it is of both the Master '75 and the Feed back 75 codes; and in the case of each of the line circuits |2--l3 and |4l5, it is of the Master '75 and the Feed back '75 codes at times and of the Master 180 and Feed back 180 codes at other times.

The single-code group of line circuits 56, 9-40, I8|9 and 22-43 of Fig. 1 will first be considered. Looking particularly at the completely represented circuits 9l0 and I 8-I9 of this group, it will be seen that each of these single-code circuits is energized from a master battery MB; that the conductors of the circuits are periodically connected with that battery by contacts 15 of the associated code transmitter CT15; and that these conductors transmit the recurring pulses of line code energy to a master line relay MR installed as shown at the opposite end of the circuit,

This master line relay MB is a code following device and in customary manner it picks up and releases in step with the on and the oif periods of the line code energy which its winding receives. This code following action, in turn, is utilized to perform certain signal control functions that later will be described.

Normally, all of the previously named singlecode line circuits are maintained intact and under that condition all of the master relays MR thereof follow code continuously. At times, however, each of these circuits is interrupted for the purpose of discontinuing the code following action just stated and thereby changing the signal governing condition in a manner later to be made evident.

For the present, it will suflice to say that in the case of line circuit 9l0 this interruption takes place at location III and is effected either by contacts 38 of a relay TP (later to be described) or by contacts 31 of a relay H (also later to be described); in the case of line circuit l8l8 the named interruption takes place at location IV and is effected either by contacts 32 of the track relay TR for section IVV or by contacts 33 of a relay Hl80 (later to be described); and so on.

The double-code group of line circuits '|8, |6l'| and 2D2i of Fig. 1 will next be considered. From an inspection of the completely represented circuit Iii-ll of this group, it will be seen that each of these double-code circuits makes use of a master battery MB at one end thereof; that the conductors of the circuit are periodically connected with this battery by contacts 15a. of the associated code transmitter CT15; and that these conductors transmit recurring pulses of master energy to a master code following relay MR at the opposite end of the circuit. For a purpose later to be made evident, thi master relay MR is polarized in the manner indicated by the plus and minus markings therefor.

The several elements just named correspond to and function in the same manner as those already described in connection with the singlecode line circuits. That is, relay MR follows the coding of the Master energy which battery MB supplies thereto over the code transmitter contacts and the line circuit conductors.

In addition, each double-code line circuit includes supplemental facilities by which the before-mentioned Feed back code is supplied and utilized. In the case of circuit |--l1 these supplemental facilities include a feed back battery FB at what will be termed the Feed back end of the circuit (which is remote from the master battery end); a similarly located feed back coder relay FC; and a feed back energized relay FR installed at what will be termed the master end of the circuit (which marks the location of the master battery MB) This master end relay PR is a code following device and it is arranged to receive operating enfront contacts 37.

The justnamed elements MR, FC and F3 at the feed back end of the line circuit cooperate'in the following manner. Each on period pulse of Master code energy that is there received from the line circuit conductors picks up the master relay MR and connects th coder relay FC with those conductors over front contact 35. Now also energized by the master energy pulse, that coder relay picks up and sets up the above-mentioned'feed'back supply circuit at That circuit, however, continues to be interrupted at the back point of contact 35.

At the end of the master code on period (and the beginning of the succeeding master code off period master relay MR releases these contacts 35 and thereby connects the feed back battery FB across the line circuit conductors over the front point of contact 3'! of the slow release coder relay FC. Once this connection is established in the manner just stated, it conready indicated, the length of each of these feed back pulses is slightly less than the length of the master code off period during which the pulse is supplied.

In the arrangement represented the master. code following relay MR is prevented from being 7 falsely picked up by thosefeed back pulses by causing the energy of which they are constituted to have an opposing polarity relation'to the recurring pulses of master code energy to which the master relay does respond. This opposing relation is indicated by the polarity markings on devices FE and MR.

ergy from the feed back battery FB at the opposite end of the circuit. During each ofi period of the Master code which the master end transmitter CTl5 produces this relay is connected with the line circuit conductors over the back points of the transmitter contacts 15a. During, however, the on periods of the thus produced master code, the same contacts disconnect the relay from the circuit conductors and thus prevent it from receiving energy from the master battery lVEB.

The feed back end coder relay FC also is a code following device and it receives pick-up energy over the front points of a pair of contacts 35 of the master code following relay MR. Under the action of a snubbing resistor 36 it is given a period of release delay which is somewhat less than the length of the master ofi periods and which is designated as k in Fig. 4.

In their released position, the same master relay contacts 35 set up a circuit over which the feed back battery is connected in energy supplying relation with the line circuit conductors. Included in this feed back supply circuit are a pair of contacts 31 of the feed back coder relay FC.

These contacts must be picked up before the supply circuit can be completed and they interrupt that circuit whenever they are released.

Each of the off period pulses of the feed back energy that is thus supplied to the line circuit in the manner above stated is transmitted over the circuit to the opposite or master end thereof. There it is impressed upon the before described feed back code following relay FR over the back points of code transmitter contacts 15a; That relay FR responds in the usual code following manner to the recurring pulses of feed back energy which its winding receives and performs signal -control functions later to be described.

It will accordingly be seen that each of the double-code line circuits (-8, iiil and 20-21 embraces the facilities of two separate coded line circuits which include the line circuit conductors as common elements and which operate simultaneously on these conductors. coded circuits transmits recurring pulses of Master code energy over the line conductors in one direction and it will be referred to as the first or Master line circuit; the other transmits off period pulses of feedback energy over the line conductors in the opposite direction and it will be referred to as the second or feed back line circuit. To designate both of. these simultaneously operating line circuits, use will be made of the expression coded feed back line circuit combination. 7

One basic application of such a combination to the rails of a track section is disclosed and One of these claimed in the before referred to Nicholson Patent 2,021,944. The present application of the coded feed back principle to line circuits is unique in that responsiveness to trafiic conditions of the associated track stretch is effected through the medium of contacts which are interposed directly in the circuit itself and which are operated by a track relay or other device of the character shown at TR in Fig. 1.

In the case of the coded feed back line circuit l6l I, such circuit interrupting contacts are represented at 39, 40, 4|, 42 and 43; in the case' of the companion two-code line circuit 18, corresponding contacts are shown at 44 and 45; and in the case of the third two-code line circuit of Fig. 1, similar traffic responsive contacts are shown at 46, 41, 4B and 49.

Normally (and as is represented in Fig. 1), all of the just named contacts are picked up and under that condition the operation of each of the coded feed back line circuits 18, |6l1 and 20--2l of the two-code group is as follows. The code transmitter CT15 at the master end recurrently picks up and releases its contact 15a at the before stated rate of 75 times per minute. Each pick-up of these contacts causes the source MB to impress'upon the line conductors a pulse of master code energy which is transmitted over those conductors to the master line relay MR at the opposite or feed-back end of the circuit.

Each pick-up of relay MR connects (over front contact 35) the feed back coder relay FC across the line conductors and causes it also to receive the master energy pulse. That relay now picks up and sets up at contacts 31 a circuit over which the feed back source FB supplies the line conductors with a pulse of feed back energy during the succeeding master code off period.

This feed back pulse is impressed upon the line conductors when contacts [511 of transmitter CT at the master end of the circuit go to their lowermost positions and thus deenergize the master relay MR at the opposite .or feed back end of the circuit. When that happens, contact 35 of relay MR disconnects the coder relay F on the line conductors and completes the above-mentioned feed back supply circuit over the back point thereof. Under this condition, battery FB transmits a pulse of feed back energy over the line conductors to the code following relay FR at the opposite or master end of the circuit.

At the end of the release period of the feed back coder relay FC, contacts 31 thereof drop out and thus terminate the feed back pulse. The apparatus at the feed back end of the line circuit is now conditioned for reception of and response to the succeeding pulse of master code energy. This pulse is supplied when the contacts 150s of the transmitter CT15 at the master end of the circuit return to their uppermost position.

When that happens the just described cycle of two direction coded line circuit operation starts to repeat itself and in the manner just outlined the master and the feed back circuit facilities operate over the line circuit conductors simultaneously and without interfering with each other.

The four-code group of line circuits l2-|3 and l b-I of Fig. 1 will finally be considered. Both of these circuits are identified with the length of track which extends between locations III and IV and which is spanned by the passing siding PS.

Each operates on the coded feed back principle which has just been explained in connection with the two-code circuits of the Fig. 1 system. Thus each includes: master and feed back batteries MB and EB at opposite ends of the line circuit; oppositely located master and feed back code following relays MR and FR which respectively are operated by energy received over the line conductors from the master and feed back batteries; a feed back coder relay FC which controls the connection of the feed back battery with the circuit conductors; and code transmitter means CT which control the connection of the master battery with the circuit conductors and also control the connection of these conductors with the feed back energized relay FR.

In the case of each of the four-code line circuits I2-l3 and l4-l5, the above-mentioned code transmitter means include not only the 75 pulse per minute code transmitter 15CT but also a companion transmitting device IBUCT the contacts of which operate at the higher rate of 180 cycles per minute. Selection between these two transmitters is made by contacts 5| of track relay TR (for section II--III) in the case of circuit |2--l3 and by contacts 52 of a relay H15 (at location IIIlater to be described) in the case of line circuit Hil5).

In the both instances these code selecting means are located at the master end of the four-code line circuits. When, as shown in the drawing, these selector contacts (5| and 52) are picked up the high speed code transmitter IBOCT performs the master code producing function for the line circuit-while when the selector contacts are released the companion or slow speed transmitter 150T is similarly brought into active use.

Since only the selected transmitter need be kept in operation the driving circuits for the two devices IBlJCT and 150T at location III are selectively energized over the front and back points of a contact 53 of the track relay TR for section IIIII. When this contact is picked up, transmitter l8flCT is brought into action and the transmitter 750T is maintained inactive. When, however, the contact is released the reversed relation applies and only transmitter 150T is maintained in operation. This same transmitter also comes into action when contact 34 of a relay HW (later to be described) is released.

Also controlled by the same contact 53 of the track relay TR at location III is the energizing circuit for the before-mentioned repeater relay TP. As long as contact 53 is picked up this repeater relay receives energy over conductor 54 and also holds all of its contacts picked up. When, however, the track relay for section IIIII releases, contact 53 breaks the energizing circuit for the repeater relay and allows that relay then to release its contacts.

Looking now at the opposite or feed back ends of the two four-code line circuits l2-I3 and I4l5, it will be seen that the added requirements of a second code following speed on the part of the master relay MR have occasioned supplemental features in connection with the snubbing circuit for the feed back coder relay FC. These take the form of a second resistor section 56 which at times is substituted for section 36 in the relay snubbing circuit.

When the master and coder relays MR and F0 are being operated at the pulse per minute code rate, a contact 51 of a code distinguishing the long delay resistor section 35 in snubbing relation with the winding of coder relay FC.

This causes the relay to have a period of release delay of the previously described order indicated at k in Fig. 4.

When, however, the master and feed back relays MR and F are being Operated at the 180 energy pulse per minute code rate, the code detecting relay contact is picked up and it then transfers the snubbing connection to the second resistor section 56. This section is so electrically dimensioned as to produce a shorter period of release delay on the part of the feed back coder relay FC. In practice this shorter period will have the order designated at x in Fig. 4 and in all instances will be somewhat less than the length of the off periods for the 180 pulse per minute master code.

Normally, both of the four-code line circuits l2-|3 and I l-I5 are maintained intact and under that condition each operates on the coded feed back principle already explained in connection with the two-code line circuits of Fig. 1. At times, however, each of these circuits is interrupted for the purpose of effecting certain signal control functions later to be described. In the case of circuit l2--|3 this interruption is effected by contacts 58, 59 and 60 of the track relays TR at locations III and IV; in the, case of line circuit I4I5 it is effected by contacts 6| of a relay HE (later to be described) at location IV;

Under the normal intact condition, each of the four-code line circuits l2--|3 and I l-45 operates in the manner basically the same as that already explained for the two-code line circuits of the Fig. 1 system. The same coded feed bac principle applies and becauseof'the basic identity no detailed description thereof will here be repeated.

For the present it will suffice to say that the selected transmitter TSCT or ISUCT repeatedly connects the line circuit conductors first with the master battery MB and then with the feed back receiving relay FR. Each of the connections first stat-ed constitutes an on period in one of the master codes of Fig. 4 and causes a pulseis transmitted over the line conductors to the.

code following relay FR at the opposite or master end of the circuit. That relay responds in conventional manner and effects the signal control functions later to be described.

If the transmitter IBEBCT is in action the rate of code following speed on the part of both of relays MR and FR will be 180 times per minute and, under that condition, contact 51 of the associated code detecting relay will connectsnubbing resistor 56 across the feed back coder relay FC. This will shorten the period of release delay to the order indicated at :c in Fig. 4, and thus assure that each pulse of feed back energy will not overlap adjacent pulses of the master code energy.

In the event that the transmitter 150T is actively functioning, then the rate of code following nects resistor 36 across the feed back coder FC and thus prolongs the period of release delay to the order indicated at k in Fig. 4. Under all conditions, therefore, the pulses of feed back, energy approach the maximum permissible length.

This and the other unique features of the fourcode line circuits 12-]3 and I l-l5 of Fig. 1' are illustrated in somewhat simplified manner in Fig. 3. In that view I have represented the several elements of line circuit l2l3 which cooperate in the coded feed back form of operation.

Control of system signals Description now having been given of the steady energy track circuits for the single track stretch of Figs. la-c and the several coded line cir-' cuits (single-code, two-code and four-code) that cooperate therewith, attention will next be directed to the facilities through which these track and line circuits control the wayside signals SE and'SW in the opposing overlap mannerof Fig. 2.

Inasmuch as these facilities differ somewhat at different locations, the control means for. each of the system signals will be described individually.

Referring first to location I of Fig. 1a and the westbound signal SW thereat, the indication which this distant? device displays is selected by the master relay MB of the previously described line circuit 56 and through the medium of a code detecting relay DW. This relay carries a contact 29 which is included in the energizing circuit'for the lamps G and Y of the controlled signal. These circuits, in turn, derive'lighting current from a local supply source designated by the terminals plus and minus.

Relay DW receives its energizing current through a transformer 25 and from a direct current source that again is designated by the terminals plus and minus. This relay is a slow releasing device and it is controlled by the line relay MR in such manner as to be maintained picked up as long as that line relay folspeed on the part of both of the relays MR and 1939, by Frank I-LNicholson et al.

rent over a pole changing contact 26 of the-line relay and the code detecting device receives pickup energy from the transformer over a rectifying contact 21 of the line relay.

In determining the aspect which the controlled signal SWI displays, this code detecting relay DW makes use of the previously named contact 29. As. long as the associated line relay MR is following code and relay DW is picked up, lamp G is lighted over the front point of contact 29.

Under this condition the signal shows clear.

When, however, the line relay ceases to follow code and device DW is released, lamp Y is lighted over the back point of contact 29 and the'signal then shows approachlf Considering next the eastbound signal SE 'at location I, the indicationwhich this homei'devicedisplays is selected by the master relayMR of the previously described line circuit l-3 through the medium of a code detecting relay HE. This relay carriesa contact 34 which is included in the lighting circuits for the lamps and R of the controlled signal. I

I This code detecting relay HE is controlled by the associated line relay MR through facilities which are identical with those just described for relay DW. These facilities keep the code detecting relay picked up as long as the line relay follows code and allow it to release when the line relay ceases to follow code. Under the former condition, lamp G of signal SEI is lighted over the front point of contact 34 and the signal then shows clear; under the latter, lamp R is lighted over the back point of contact 34 and the signal then shows stop.

Referring now to location II of Fig. 1a, it will be seen that the westbound home and the eastbound distant signals SWII and SEII thereat respectively are controlled through the medium of code detecting relays HW and DE which, in turn, are respectively governed by feed back and master line relays FR and MR of line circuits |8 and 9IB. Each of these code detecting relays is associated with a transformer and the controlling line relay in the same manner as that disclosed and claimed by the previously mentioned Frank H. Nicholson et a1. application Serial No. 210,744.

As long, therefore, as relay FR at location II is following code detecting relay HW is held picked up to light (over the front point of contact 34) the clear lamp G of signal SWII; when, however, relay FR ceases to follow code, detecting relay HW releases and stop lamp R of the named signal then is lighted over the back point of contact 34.

Similarly, as long as relay MR at location II follows code, detecting relay DE is held picked up to light (over the front point of contact 29) the clear lamp G of signal SEII; when, however, relay MR ceases to receive coded energy from line circuit 9l0, detecting relay DE releases and approach lamp Y of signal SWII then is lighted over back contact 29.

At location III of Fig. 1a the home westbound signal SWIII is controlled through a code detecting relay HW and by a feed back line relay FR which, as in the case of relay FR at location II, also receives operating energy from line circuit 'I8. As long as this feed back energy continues to be received over the back points of contacts 75a of transmitter 150T, this relay HW is held picked up and clear lamp G of signal SWIII is lighted over front contact 34; when, however, relay FR ceases to follow code, relay I-IW releases and stop lamp R of signal SWIII then is lighted over back contact 34.

Referring to signal SEIII at location III, it will be seen that this signal includes a"home unit RG and a distant unit YG. These two units respectively are controlled through relays HE and DE at the signal location and by the feed back code following relays FR and FRI of line circuits |2-l3 and I4l5.

Each of the just named code detecting. relays HE and DE has response characteristics which are'the same as those already described in connection with similarly identified devices at locations I and II. In the case of. the home unit RG of signal SEIII the clear lamp G is lighted as long as the line relay FR continues to follow feed back code from line circuit l2l3 of either the 75 or the 180 pulse per'minute rate,

'while the stop lamp R is lighted when relay long as relay FRI continues to receive from line circuit l 4-I5 feedback code of either the 75 or the 180 pulse per minute variety, while the approach lamp Y of the same signal is lighted when line relay FRI ceases to follow code.

At location IV of Fig. lb, the eastbound home signal SEIV is controlled through code detecting relay HE and by the feed back relay FR of line circuit Iii-l1. As long as this relay FR continues to respond to feed back code received from the just named line circuit, detecting device HE is picked up and clear lamp G of the controlled signal is'lighted over front contact 34; when, however, relay FR ceases to follow code, device I-IE releases and lights stop lamp R of signal SEIV over back contact 34. i

As in the case of eastbound signal SEIII at location III, the westbound signal SWIV at location IV includes a home unit G--R and a distant unit G-Y. The former is controlled through a code distinguishing relay H180 and by the master relay MR of line circuit l2-I3,

while the latter is controlled through a second code distinguishing relay Dl and by the master relay MRI of line circuit l4--l5.

Each of the just named code distinguishing relays receives its pick-up energy from a decoding transformer DT which, in turn, is excited from a local direct current source over a circuit that is controlled by a pole changing contact 26 of the associated code following line relay MR. The secondary Winding of this decoding transformer is connected in energy supplying relation with the code distinguishing relay through a resonant unit I80DU which permits energy of pick-up intensity to be transmitted to the relay only when the master line relay MR responds to operating energy of the pulse per minute code.

Hence, the elements just named cooperate to cause the code distinguishing relay Hi8!) to pick up when the master relay MR of line circuit I2-l3 is operating at the 180 code rate and to release at all other times. Likewise, they cause the code distinguishing relay DIED to pick up only when master relay MRI is responding to 180 pulse per minute code received from line circuit I4-,- l5 and to release at all other times.

In determining the aspect which is displayed by the home and distant units of the controlled wayside signal SWIV, the above described code distinguishing relays make use of contacts 34 and 29. When contact 34 is picked up clear lamp G of the home unit then is lighted, while when the same contact is released the stop lamp R of the same unit is lighted. Similarly, when contact 29 is picked up the clear lamp'G of the distant unit is lighted, while when contact 29 is released the approach lamp Y of the same unit is lighted.

Referring to location V, the distant westbound signal SWV thereat is controlled through a code detecting relay DE and by the code following relay MR of line circuit I8|9. As long as this line relay follows code the detecting device is picked up and front contact 29 then sets up a lighting circuit for the clear lamp G of the controlled signal. When, however, relay MR ceases to follow code then relay DE releases and back contact 29 sets up a lighting circuit for the approach lamp Y of the signal.

In order for either of these circuits to becompleted it is necessary that a contact 64 of an approach lighting relay AR be released. This approach relay is installed at the location of the controlled signal in the manner shown and it derives pick-up current from a full'wave rectifier 65 that is serially connected in one of the conductors of line circuit [-41. The relay has slow releasing characteristics and as long as the named line circuit transmits the coded energy of either the master or the feed back variety the relay is held picked up to keep the associated wayside signal SWV dark.

In the event, however, that the line circuit I 6-1 '1 becomes interrupted at any point between its end locations IV and VII then relay AR at location V becomes released and connects the lighting circuits of signal SWV with their energizing source. Under that condition, the signal responds in the manner explained to the position of contact 29 of code detecting relay DE.

At location VI the home eastbound signal SEVI is provided with comparable control facilities. These include an indication selecting relay HE governed through transformer 25 by code following relay MR of line circuit 28-2l and an approach relay AR which in all respects is a duplicate of the correspondingly identified device just described atlocation V.

As long as line circuit l5l'i continues to transmit coded energy this approach relay is picked up and the associated wayside signal SEVI then remains inactive or dark. When} however, the just named line circuit is interrupted relay AR becomes deenergized and the back point of contact 64 then connects the lighting circuits of the associated signalwith their energizing source.

Under that condition, the signal responds to the presence or absence of code following action on the part of relay MR of line circuit 2ii-2l. When this relay is following code, contact 34 of device HE. completes the lighting circuit for clear lamp G of the signal, while when relay MR is not following code the back point of contact 3:2 completes the stop or red lamp circuit for signal SEVI.

In the case of home westbound signal SWVII at location VII 9. corresponding scheme of control is provided. The facilities thereof include an indication selecting relay HW which distinguishes the presence or absence of code following operation on the part of the masterrelay MR of line circuit 16-41 and an approach relay AR which distinguishes the presence or absence of coded energy in line circuit 2il 2l.

As long as energy is being transmitted by this line circuit 20,-2 I, relay AB, is picked up and contact 64 thereof keeps the lighting circuits of signal SWVII disconnected from their energizing source. In the event, however, that the just named line circuit is interrupted at any point throughout its length, relay AR at location VII releases and conditions the signal SWVII for response to the position of contact 34 of relay I-IW at the same location. Under that condition the signal shows clear when relay MRof line circuit lS-ll is followingcode and stop when that master line device ceases to follow code.

Referring finally to the distant eastbound signal SEVIII at location VIII, the control facilities for this device also correspond to those which have just been explained. They include an indication selecting relay DE which detects the presence of code following operation on the part of relay MR of line circuit.22-2S and an approach relay AR which maintains the signal inactive as long as line circuit 2B--2l continues to transmit coded energy and which connects the selected signal lamp with its lighting source when and only when the transmission of that energy is discontinued. Under the latter condition the signal shows clear when the relay MB, of circult 22-23 is following code and approach when the just named relay ceases to follow code.

Operation of complete system of Figs. Za-o The apparatus and circuits which are utilized in the coded line circuit signal control system of Figs. la-c now having been described, the manner in which this system operates to provide both directional and following protection for trains which move through the stretch of single track 1-2 will now be explained. As an aid to this explanation, further reference will be had to the control limit and code diagrams of Figs. 2 and 4.

In explaining this operation, typical moves of eastbound trains through the stretch will first be traced and the following protection which is incident thereto will be pointed out; representative moves of westbound trains through the stretch will then be traced for the purpose of explaining the following protection which is incident thereto; and finally opposing moves will be considered in the light of the directional protection which the overlap signal control scheme provides.

Under the represented vacant conditions of the track stretch of Figs. la-c, all of the track relays TR are picked up; all of the coded line circuits in the system are transmitting energy in the manner previously explained; all of the line relays MR and FR are following code; all

- of the indication selecting relays DW, HW, DE,

HE, D580 and H188 are picked up; all of the approach relays AR. also are picked up; and each of the wayside signals SE and SW is either dic playing or set up to display the clear indication.

In considering the following protection which the system provides, it will be helpful to note that the track and line circuits that are identifled with the Various sections of track in the protected stretch form part of two systems which respectively control in the customary automatic block manner the eastbound signals SE during conditions of eastbound moves and the westbound-signals SW during conditions of west In the form illustratively reprethe eastbound signal SE which isthere installed.

. gizing source.

leases and puts signal SEI at stop. This stop As the train advances past location I and releases the track relay TR at location II, contacts 4 4 of that relay break line circuit 'I-B and disconnect the relay MR at location I from its ener- The associated relay HE now redisplay continues until the train has cleared location II.

In entering section II-III the train releases relay TR at location III and thus causes the repeater device TP to drop contacts 36. That action deenergizes relay MR at location II and by releasing the associated relay DE puts eastbound signal SEII at approach. This approach display continues until the train clears location III. When that happens, relay TR for section IIIII again picks up and by restoring the continuity of line circuits 1-8 and 9ID causes both of the wayside signals SEI and SEII to return to clear.

In entering signal block III-IV, the eastbound train causes one of the associated track relays TR to break. line circuit I2-I3 and thus it deenergizes feed back relay FR at location III. This action drops the associated relay HE and puts at stop" the home unit of eastbound signal SEIII. This aspect continues until the train clears location V and thus allows both of the track relays TR at location IV to pick up and restore the supply of feed back energy to relay FR at location III. Upon such restoration, the associated relay HE picks up and restores the home unit of signal SEIII to clear.

In advancing into section IVV the train releases the track relay TR for that section and breaks line circuit l6l'| at contact 39. This break deenergizes relay FR at location IV and by dropping relay HE puts eastbound signal SEIV at stop. At the same time, contacts 6| of relay HE out ofi the supply of feed back energy to relay FRI at location III and by dropping relay DE put the distant unit of signal SEIII at approach. This aspect also continues until the train clears locationV.

As the train enters section V-VI and approaches signal SEVI, one or the other of relays TR for the section keep line circuit I 6-H interrupted and thereby release relay AR at location VI. This causes signal SEVI to display the clear indication for which it is setup by the associated relay HE.

In entering section VIVII the eastbound train releases relay TR .for that section and breaks (at contacts 41) the line circuit 20-2I'. This break deenergizes relay MR and by releasing relay HE causes signal SEVI to show stop. Once established, this stop aspect continues until the train clears location VIII.

In approaching that location, the train brought signal SEVIII into action as the result of the before explained interruption of line circuit 202| at the contacts of track relays TR and the resulting release of relay AR at' location VIII. In consequence, signal SEVIII displays the clear indication which relay DE sets up. As the train passes location VIII, track relay means (not shown in Fig. 1c) interrupt line circuit Z2-23 and by deenergizing relay MR and releasing relay DE cause eastbound signal SEVIII to show approach.

From the foregoing it will be seen that during eastbound train movements through the protected stretch the just explained scheme of automatic block signaling provides the usual following protection which maintains a safe spacing between successive eastbound trains. That is, as long as an advance trainoccupies (and shunts the rails of) a signal block of the system track, the wayside signal SE at the west (eastbound entrance) end of that block is conditioned to show stop and succeeding signals SE to the tion with eastbound moves.

west are conditioned to show either approach or clear. As, moreover, the train moves eastwardly along the rails the above stated combination of signal indications continues to be maintained behind it and in this way following protection for eastbound moves is at all times provided.

Westbound train moves through the protected stretch of Figs. la-c will now be considered. Each westbound train which passes along the track automatically sets up for itself following protection of the character just described in connec- This following protection results from the actions which will now be described in tracing the passage of a westbound train through the stretch.

Under vacant conditions of the protected stretch, the several westbound signals SW therealong have the condition represented in the composite diagram of Figs. lot-c. Each either displays or is set up to display the clear indication as a result of the associated track relays TR being picked up and the associated line circuits transmitting coded energy in the normal manner.

As, now, a westbound train enters the stretch from the right and comes into section VIII-VII it causes westbound signal SWVII to light and display the clear indication set up by the associated relay HW. The mentioned lighting is produced by the release of relay AR at location VII which accompanies the interruption of line circuit 2E2l by one of the relays TR.

As the westbound train moves on into block VII-V, relay TR at location VI interrupts line circuit l6l1 and by deenergizing relay MR at location VII and releasing the associated relay I-IW puts signal SWVII at stop. Once set up, this aspect continues until the train has cleared location V. In approaching location V, the westbound train gets from signal SWV the clear indication whichthe associated relay DE sets up and which the now released relay AR makes visible. This release of the approach relay results, of course, from an interruption of the line circuit lB-l'l at the contacts of one of the track relays TR.

As the train enters section VIV, it causes relay TR at location IV to interrupt line circuit l8l9. This action deenergizes relay MR at location V and by releasing relay DE puts westbound signal SWV at approach. This aspect continues until the train has cleared location III, at which time the signal SWV is returned to the clear aspect set-up.

In approaching location IV, the westbound train gets the clear indication from signal SWIV as a result of both of the associated relays Dl8ll and HIBO being held picked up under the action of Master I code energy being transmitted eastwardly over line circuits I2-l3 and As the westbound train moves into block IVIII, the home unit GR of the just named signal shows stop as a result of relay TR at location VI interrupting line circuit l'2|3 and causing relay I-II80 to release. This stop" aspect continues until the train has cleared location II.

In accepting the clear indication from signal SWIII the train moves on into section III-II. At location III this releases relays TR and TP and by deenergizing relay FR of line circuit l-8 drops out the associated relay I-IW and thus puts westbound signal SWIII at stop. That action is accompanied by a release of contacts 52 of relay HW and a substitution in each of the line circuits l2l3 and I i-l5 of code transmitter 750T for the normally active transmitter lBBCT.

At location IV, relay man now releases (due to the slowed down code following action of relay MRI) and thus puts the distant unit of signal SWIV at approach. At the same time, relay I-IIBO also continues released and holds the home unit of the same signal at stop.

In accepting the clear indication from signal SWII the westbound train advances into section III. This action releases track relay TRat location II and by breaking line circuit 'l8 at contacts 4 3 deenergizes feed back relay FR at the same location. The associated relay HW now releases and puts signal SWII at stop.

As the train clears location II, relay TR picks up and restores the coding of line circuit l2l3 to transmitter l8i'lCT. At location IV, this causes the pick-up of relay Hist and the restoration of the distant unit G-Y of signal SWIV to its clear indication.

In accepting the clear indication from signal SWI, the westbound train advances West of location I. In so doing, it causes (through facilities not shown in Fig. 1a) the interruption of line circuit 56 and by deenergizing relay MR and releasing relay DW puts signal SWI at approach.

As the train clears location I, relay TR at location II restores (at contacts it) the continuity of line circuit 1-8 and thus causes relay FR at location III again to receive coded feed 5 tant unit G-Y of signal SWIV to its clear indication.

From the foregoing, it will be seen that the just described westbound scheme of automatic block signaling provides the usual following protection for all westbound train moves. as long as a westbound train occupies (and shunts therails of) a section of the system track, the wayside signal SW at the east (westbound en- That is,

trance) end of that section continues to show stop and the next signal SW to the east is continuousiy conditioned to show either ap proach or clear. As, moreover, the train moves westwardly along the rails, the above stated combination of signal indications continues to be maintained behind it and in this way following protection for westbound trains is at all times provided.

Overlap protection during opposing moves In addition to providing the protection which I cuits for preselected homefsignals beyond the next signals in advance, which govern in the same direction, at least full braking distance and making the continuity of these circuits dependent upon the condition of the track sections ahead of those advance signals. As previously pointed out, moreover, one preferred form of such overlap signal control is shown in Fig. 2.

In the explanation now about to be given, reference will be made not only to the composite diagram of Fig. 1 but also to this control limit diagram of Fig. 2. From the latter it will be seen that the home unit R-G of eastbound signal SEIII has an advance control range which extends not only to the next home signal SEIV ahead but also for the length of section IVV; that eastbound signal SEIV has an advance conrol range which extends not only to the next home signal SEVI ahead but also for the further combined lengths of sections VIVII and and VII -VIIa; that the westbound home signal SWVII has an advance control range which extends beyond the next signal SWV in advance for the distance of section V--IV;

has an advance control range extending beyond the next signal SWIII for the length of section IIIII; and so on.

Assume now that an eastbound train is appreaching location III from the west at the same time that a westbound train is approaching. location V from the east. Obviously, one of the two trains must be diverted to the passing siding PS while the other proceeds therepast along the main track l2 and the embodiment of my invention 1 herein disclosed provides full protection during such a passing maneuver.

As long as the eastbound train stays to the west of location III and the westbound train stays to the east of location V, each of these trains gets a permissive indication from the signal (SEIII and SWV) that is immediately ahead. In the case of the eastbound signal SEIII, this indication is clear, it is displayed by the unit YG, and it results from the transmission over line circuit Mi5 of feed back energy to code following relay FRI at location III. In the case of westbound signal SWV, the permissive indication is approach and results from line circuit iti9 being interrupted at contacts 33 of code distinguishing relay Hitfi of the line circuit iZ-i3.

This approach indication warns the westbound train that the track ahead is occupied by an opposing eastbound train and'require's that the westbound train proceed with caution. Meanwhile, the eastbound train is free to accept the clear indication 'at location III and to proceed therepast into block III-IV.

It will be assumed that under the authority of a train order the eastbound train is switched to passing siding PS and in the usual manner is entirely removed from the main track '|2. During all of this time some portion of the eastbound train is shunting section IIIIIIa and thus causing line circuit 52i3 to be interrupted at contacts 53 of relay TR. This interruption continue the stop indication on the part of the home unit GR of the westbound signal SW at location IV. As, therefore, the westbound train approaches that signal it is warned not to enter block IVIII.

Meanwhile, the eastbound train has complete- 1y left the main track l2 and is all on the passing siding PS. With the restoration of the switches W to the normal through traflic posithat the home unit RG of westbound signal SWIV tion, the rails throughout the entire block IVIII are unshunted and both of the associated track relays TR pick up. This action restores line circuit l2l3 to its completed condition and as a result of the transmission of Master I80 code eastwardly thereover, code distinguishing relay Hi8!) again picks up and restores the clear aspect to Westbound signal SWIV.

Accepting this aspect, the westbound train enters the block IVIII and proceeds therethrough under the usual vacant track conditions. This having taken place, the eastbound train is advanced from the passing siding PS back on to the main track l--2. It accepts the clear indication from eastbound signal SEIV and proceeds therepast, also under the usual vacant track conditions.

In the manner just stated, therefore, opposing trains are permitted to pass one another under full automatic protection against head-on collision. While the maneuver just described requires that the eastbound train take to the passing siding, a passing of the two trains may also be accomplished by keeping the eastbound train on the main track and having the westbound train take to the siding.

Such a modified passing maneuver will now be described. First assume that the eastbound train is approaching location II at a time when a westbound train is approaching location IV. Under this set of circumstances each of the two trains receives the clear indication from the wayside signal (SEII and SWIV) which is immediately thereahead.

In the case of the eastbound signal SEII, this clear indication results from line circuit 9l0 being kept intact and transmitting coded energy in the normal manner, while in the case of the home and the distant units G-R and G-Y of the westbound signal SWIV it similarly results from. line circuits I2-l3 and. I i-l transmitting Master I80 code energy in the normal vacant track manner.

At location III, the just stated indications are accompanied by the display of stop on the part of eastbound signal SEIII. This stop aspect is given by the home unit R-'-G and results from the action of relay TR for section V-IV in cutting off (at now released contact 60) the transmission of feed back energy over line circuit |2-l3 to the code following relay FR. at location III.

Accepting the clear indication at location IV, the westbound train proceeds therepast and enters block IVIII. Under train orders, it takes to the passing siding PS preparatory to clearing the main track l2 for a later passage thereover of the eastbound train. Meanwhile, some portion of the westbound train continues to shunt section IVIIIa and by interrupting the line circuit I 2I3 at contacts 59 causes eastbound signa SEIII to continue to show stop.

Once the westbound train has completely left the rails of section IVIIIa by the westbound train put the eastbound signal SEII at .approach. scribed release of relay HlE at location III and This resulted from the before de-.

the consequent interruption at contacts 3| thereof of line circuit 9|0. That approach indication at location II continued only as long as the westbound train was entering the passing siding PS. With the later shunt removal from the rails of block IVIII, contacts 3| of relay 'HE at location III again restored line circuit 9-I0 to its operative condition and thus caused signal SEIII again to show clear.

Accepting this clear indication, the eastbound train now proceeds into section II-III and gets the before described clear indication from signal SEIII. Accepting that indication, it proceeds into and through block IIIIV in the usual vacant track manner.

Once the eastbound train has cleared location IV, the westbound train is free to advance from the passing siding PS back on to the main track [-2 and out of block IVIII in the usual vacant track manner.

In the further manner stated, therefore, it will be seen that my improved overlap signaling scheme permits opposing trains to pass one another under full automatic protection against head-on collision.

It is believed that the opposing move analysis thus far given will be suflicient to make clear how all of the line circuit governed signals of Fig. 1 are controlled in the overlap manner which is represented by the control limit diagram of Fig. 2. For this reason, no further description of the here disclosed control facilities will be attempted.

When organized in the improved manner of my invention these facilities offer many advantages which are both desirable and practical. For example, they protect against improper signal operation due to an accidental crossing or breaking of the line circuit conductors. By interrupting transmission of the coded line circuit energy either of those actions causes the controlled signal to display its most restrictive or stop aspect and because of that characteristic the signaling system as a whole has a high inherent factor of safety.

Summary While the improvements of my invention have been disclosed in connection with an opposing overlap scheme of automatic signaling for two direction running track, it will be apparent that the disclosed type of control is not necessarily confined to the overlap application but may also be used with other forms of single track signaling, such as those which involve the absolute permissive block (APB) scheme of signal control. Likewise, while the several coded feed back line circuit combinations in the system have been shown as receiving operating energy from the direct current sources MB and FE, it will further be apparent that these same line circuits (see the simplified showing of Fig. 3) may readily be modified to operate on alternating current. Still further, while the controlled signals are shown as being of the color light type, it is equally apparent that further classes of signals may also be controlled by this general scheme of line circuit organization.

From the foregoing, accordingly, it will be seen that I have made highly practical improvements in line wire signaling systems for stretches of railway track over which traffic may move in either direction.

In particular, I have reduced the number of control conductors which line wire systems of railway signaling require; I have utilized a single pair of line wires to control signals that govern trafiic in either direction; I have provided new and improved facilities for overlapping the track circuit control limits of the system signals; I have protected against improper signal operation due to an accidental crossing or breaking of the system line wires; I have made a new and novel application of the coded feed back principle of Frank. H. Nicholson Patent No. 2,021,944; and I have provided improved apparatus for use in line and other circuits of the coded feed back type.

Although I have herein shown and described only one form of signaling apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination, a control circuit which includes a pair of conductors, means at a given end of said circuit for supplying said conductors with master code energy in the form of on period pulses that are separated by ofi period intervals and that recur at a high speed rate at times and at a low speed rate at other times, a code following master relay at the opposite end of said circuit which responds only to the pulses of said master code energy that are there received, a similarly located source of feed back energy, a coder relay which is picked up by said master relay during each on period of said received master code and which releases during each succeeding 01? period of that code, means including a back contact of said master relay and a front contact of said coder relay for connecting said feed back source with said circuit conductors at the beginning of each of said oil a code periods whereby to supply said conductors with a pulse of feed back energy during each of those off periods, means effective when said received master code is of said high speed variety for delaying each release of said coder relay for a time just less than the off period length of that high speed code whereby each of said feed back pulses then is prolonged for substantially its full permissible duration, means effective when said received master code is of said low speed variety for delaying each release of said coder relay for a time just less than the off period length of that low speed code whereby each of said feed back pulses then also is prolonged for substantially its full permissible duration, and traiiic governing apparatus controlled by the said feed back energy which said conductors transmit to said given end of the control circuit.

2. In combination, a control circuit which includes a pair of conductors, means at a given end of said circuit for supplying said conductors with master code energy in the form of on period pulses that are separated by off period intervals and that recur at a high speed rate at times and at a low speed rate at other times, a code following master relay at the opposite end of said circuit which responds only to the pulses of said master code energy that are there received, a coder relay which is picked up by said master relay during each on period of said received master code and which releases during each succeeding off period of that code, means effective when said received code is of said high speed variety for delaying each release of said coder relay for a time less than the off period length of that high speed code, means effective when said received code is of said low speed variety for delaying each release of said coder relay for a time longer than that just named but less than the off period length of the low speed code, a source of feed back energy at said opposite circuit end, a connection including a backcontact of said master relay and a front contact of said coder relay over which said feed back source supplies feed back energy to said control circuit conductors during each ofi period of whichever of said two master codes said master relay receives, and trafiicgoverning apparatus controlled by the said feed back energy which said conductors transmit to said given end of the control circuit.

3. In a system of railway signaling, a control circuit which includes a pair of conductors, means at a given end of said circuit for supplying said conductors with master code energy in the form of on period pulses that are separated by off period intervals and that recur at a high speed rate at times and at a low speed rate at other times, a code following master relay at the opposite end of said circuit which is energized and picked up byeach pulse of said master code energy that is there received, a coder relay which is picked up by said master relay during each on period ofsaid received master code and which releases during each succeeding off period of that code, snubbing means for said coder relay which include a first element that produces a short release delay less than the oif period length of said high speed code and a second element that produces alonger delay less than the off period lengtheof said low speed code, means governed by said master relay for rendering said short delay element effective when the master relay is responding to said high speed code and for rendering said longer delay element efiective whenthe master relay is responding to said low speed code, a source of feed back energy at said opposite circuit end, a connection including a back contact of said master relay and a front contact of said coder relay over which said feed back source supplies feed back energy to said control circuit conductors during each off period of whichever of said two master codes said master relay receives, means for rendering said master relay unresponsive to the said energy which said feed back source supplies, and trafiic governing apparatus controlled by the said feed back energy which said conductors transmit to said given end of the control circuit.

4. In combination, a section of railway track, a control circuit which is coextensive with said section and which includes a pair of line conductors, means at a given end of said circuit for supplying said conductors with master code energy in the form of on period pulses that are separated by off period intervals and that recur either at a high speed rate or at a low speed rate, a code following master relay at the opposite end of said circuit which responds only to the pulses of said master code energy that are there received, a coder relay which is picked up by said master relay during each on period of said received master code and which releases during each succeeding off period of that code, snubbing means effective when said received master code is of said high speed variety for delaying each release of said coder relay for a time less than the off period length of that high speed code, other snubbing means effective when said received master code is of said low speed variety for then delaying each release of said coder relay for a time longer than that lust named but less than the off period length of the low speed code, a source of feed back energy at said opposite circuit end, a connection including a back contact of said master relay and a front contact of said coder relay over which said feed back source supplies feed back energy to said line conductors during each ofi period of whichever of said two master codes said master relay receives, means responsive to the presence of a train in said section for causing said line conductors .to discontinue energy transmission between said two circuit ends, traffic governing apparatus controlled by the said master code energy which is received at the said opposite circuit end, and other traffic governing apparatus controlled by the said feed back energy which is received at said given circuit end.

5. In combination, a stretch of railway track which is arranged into successive track sections and over which trafiic may pass in either direction, a signal block length of said track which embraces at least one of said sections, first and second signals respectively identified with opposing ends of said block and respectively arranged to govern the entry thereinto of first directicn trains and of second direction trains, a control circuit that includes a pair of line conductors which are coextensive with said block, means at the first signal end of said control circuit for supplying said conductors with master code energy in the form of recurring pulses that are separated by off period intervals, means at the second signal end of said control circuit which receive said master code pulses and Which cause said second signal to display its clear aspect as long as said reception continues and a restrictive aspect when that reception is interrupted, similarly located means which further supply said circuit conductors with pulses of feed back energy that recur in step with the off period intervals of said received master code, means at the first signal end of said control circuit which receive said feed back pulses and which cause said first signal to display its clear aspect as long as said reception continues and a restric tive aspect when that reception is interrupted, means effective whenever a train is in said signal block for interrupting said line circuit and thereby then producing a restrictive aspect on the part of each of said first and second signals, and means effective whenever a train is in the section over which second direction traflic approaches said second signal for discontinuing the supply of said feed back energy to said line circuit whereby then also to produce a restrictive aspect on the part of said first signal.

6. In combination, a stretch of railway track which is arranged into successive track sections and over which traffic may pass in either direction, a signal block length of said track which embraces at least one of said sections, first and second signals respectively identified with opposing ends of said block and respectively arranged to govern the entry thereinto of first direction trains and of second direction trains, a control circuit that includes a pair of line conductors which are coextensive with said block, means at the first signal end of said control circuit for supplying said conductors with master code energy in the form of on period pulses that are separated by ofi period intervals and that recur at a first rate normally and at a second rate at certain times, means at the second signal end of said control circuit which receive both said first and second rate pulses of master code energy and which cause said second signal to display its clear aspect when and only when said first rate pulses are received and a restrictive aspect at all other times, similarly located means which further supply said circuit conductors with pulses of feed back energy that recur in step with the off period intervals of the received master code, means at the first signal end of said control circuit which receive said feed back pulses and which cause said first signal to display its "clear aspect as long as said reception continues and a restrictive aspect when that reception is interrupted, means effective whenever a train is in said signal block for interrupting said line circuit and thereby then producing a restrictive aspect on the part of each of said first and second signals, means effective whenever a train is in the section over which first direction traific approaches said first signal for causing said there supplied pulses of master code energy to recur at said second rate whereby then also to produce a restrictive aspect on the part of said second signal, and means effective whenever a train is in the section over which second direction trafiic approaches said second signal for discontinuing the supply of said feed back energy to said line circuit whereby then also to produce a restrictive aspect on the part of said first signal.

'7. In combination, a stretch of railway track which is arranged into successive track sections, a signal block length of said track which embraces at least one of said sections, first and second signals respectively identified with opposing ends of said block and respectively arranged to govern the entry thereinto of first direction trains and of second direction trains, a control circuit for said first signal which includes a pair of line conductors that are coextensive with said signal block length i of track plus the section which adjoins the second signal end of that block, means effective under vacant conditions of both said block and said adjoining section for transmitting over the conductors of said line circuit coded current which causes said first signal to display a proceed indication, an approach relay serially connected in one of said line conductors and held continuously picked up by the said coded current which flows through that conductor, means controlled by said approach relay for supplying energizing current to said second signal when and only when that relay is released, and means responsive to the presence of a train in either said signal block or said adjoining section for interrupting said line circuit whereby then to cause said first signal to give a restrictive indication and whereby then also to release said approach relay and render said second signal active.

HOWARD A. THOMPSON. 

